Crutch with adjustable handgrip

ABSTRACT

The metal tubular shaft of a single-shaft crutch is locally reinforced by a slidable sleeve of substantial length that embraces the shaft and the sleeve carries a laterally extending handgrip. The sleeve is adjustable along the shaft to vary the distance of the handgrip from the upper end of the shaft. The length of the sleeve is not less than the distance from the axis of the shaft to the center of the applied load on the handgrip and therefore the lateral force transmitted to the shaft at each of the two ends of the sleeve is not more than the applied load.

United States Patent [1 1 Smith Oct. 30, 1973 CRUTCH WITH ADJUSTABLE HANDGRIP [76] Inventor: Alfred A. Smith, 8277 Lankershim Blvd., North Hollywood, Calif. 91605 [22] Filed: June 11, 1971 21 Appl. No.: 152,166

[52] U.S. Cl. 135/51, 135/50 [51] Int. Cl A6lh 3/02 [58] Field of Search 135/52, 51, 50, 49

[56] References Cited UNITED STATES PATENTS 190,392 5/1877 Weldon 135/50 254,348 2/1882 Maine 135/51 1,331,109 2/1920 Hunter..." 135/51 2,172,047 9/1939 Jac0bucci.... 135/50 2,228,592 1/1941 Curtis 135/50 X 3,429,409 10/1947 Eidman 135/51 2,568,654 9/1951 Neptune 135/49 X 2,736,330 2/1956 Wood 135/52 X 2,771,089 11/1956 Magida 135 50 2,817,348 12/1957 Holliday 135/47.5

FOREIGN PATENTS OR APPLICATIONS 675,275 7/1952 Great Britain 135/49 242,287 12/1962 Australia l35/47.5 118,446 8/1918 Great Britain 135/52 Primary Examiner-Dennis L. Taylor Attorney-Smyth, Roston & Pavitt [57] ABSTRACT The metal tubular shaft of a single-shaft crutch is 10- cally reinforced by a slidable sleeve of substantial length that embraces the shaft and the sleeve carries a laterally extending handgrip. The sleeve is adjustable along the shaft to vary the distance of the handgrip from the upper end of the shaft. The length of the sleeve is not less than the distance from the axis of the shaft to the center of the applied load on the handgrip and therefore the lateral force transmitted to the shaft at each of the two ends of the sleeve is not more than the applied load.

8 Claims, 19 Drawing Figures PAIENIEllm 30 ms 3.7682195 SHEET 2 OF 3 I W n raz- 1409194 /7. 501/74 CRUTCH WITH ADJUSTABLE I'IANDGRIP BACKGROUND OF THE INVENTION This invention relates to a single-shaft tubular crutch of the type disclosed in the Wood US. Pat. No. 2,736,330. Such a crutch has a handgrip mounted on the shaft at an intermediate level to bear a substantial portion of the weight of the user and the crutch is adjustable in overall length as well as adjustable both with respect to the distance of the lower end of the shaft from the handgrip and the distance of the upper end of the shaft from the handgrip.

In order to mount the handgrip rigidly on the shaft, the handgrip of the above crutch is made integral with a collar that embraces the shaft. The axial dimension of the collar is relatively short, being comparable to the thickness of the handgrip. To permit adjustment of the handgrip longitudinally of the shaft, the collar is slidingly mounted on the shaft and is releasable tightened against the shaft.

The short axial dimension of the collar is important in the transmission to the shaft of forces created by the weight imposed by the user on the handgrip. For the purpose of calculation it may be assumed that the weight is applied to the midpoint of the length of the handgrip so that the length of the moment arm that receives the load is the distance from the midpoint of the handgrip to the axis of the shaft.

The load that is transmitted to the handgrip by the user is transmitted by the collar to the shaft as two opposite lateral forces against the shaft at the two opposite ends respectively of the collar. In the crutch disclosed in the above mentioned patent, the collar on which the handgrip is mounted is so short that the unavoidable consequence is that the collar actually multiplies the force it receives from the handgrip. This fact increases the possibility that the shaft will be marred if not permanently deformed and it also increases the possibility that troublesome play or looseness will develop between the collar and the shaft to make it frequently necessary to tighten the collar against the shaft.

It would be highly desirable for the short collar of the Wood crutch to be easily and quickly adjustable along the tubularshaft of the crutch to vary the distance of the handgrip from the upper arm rest. For example, the collar could beprovided in a well known manner with a manually retractable spring-pressed locking pin that is capable of selectively engaging a series of radial locking bores in the wall of the tubular shaft. Since the" collar must be slidable for adjustment, however, such a construction would require that the collar have an appreciable degree of looseness when in locked position, whereas any perceptible looseness when the collar is locked would be intolerable. The force-multiplying effect caused by the relatively short axial dimension of.

With reference to looseness or play between the handgrip and the crutch shaft, it is to be noted that a collar that is short enough to multiply the force that is transmitted to the shaft also has a motion-multiplying effect in the reverse direction in that clearance of a given magnitude between the two ends of the collar and the shaft permits corresponding backlash which is multiplied in the backlash movement of the handgrip when the load on the handgrip is periodically reversed. Thus, a relatively short collar not only increases the forces that tend to deform the crutch shaft but also increases the play of the handgrip relative to the shaft.

To meet this problem of making the collar adjustable along the shaft without looseness of the handgrip when the crutch is in use, the handgrip of the crutch disclosed in the Wood patent is made rigidly unitary with the collar and a set screw inside the handgrip on the axis thereof is releasably tightened against the shaft to prevent backlash. Unfortunately, the set screw must be severly tightened against the shaft in a damaging manner. Sever tightening is necessary to eliminate looseness of the handgrip and sever tightening is also necessary because the set screw actually carries the weight that is imposed on the handgrip by the user and therefore must be tight enough to prevent slippage.

The unloosening and subsequent tightening of the set screw that is involved in changing the elevation of the handgrip is not only time consuming but also requires considerable strength and effort on the part of the user. There is a definite need, therefore, for a crutch construction wherein the handgrip is quickly and conveniently locked at selected positions of adjustment by means that makes positive engagement with the shaft instead of frictional engagement and wherein the problem of backlash is solved in a satisfactory manner.

SUMMARY OF THE INVENTION A primary object of the invention is to solve the problem of making the handgrip quickly and conveniently adjustable by means that makes positive engagement with the shaft and to solve the related problem of avoiding marring and deforming the shaft, together with the related problem of avoiding disturbing play between the handgrip and the shaft.

This primary object is obtained by two structural provisions that distinguish the invention from the type of crutch that is disclosed in the Wood patent. The first distinction is that the handgrip is fixedly mounted on a reenforcement sleeve which is at least equal to the length of the moment arm of the handgrip as measured from the axis of the shaft to the midpoint of the length of the handgrip. Making the adjustable reinforcement sleeve of this minmum length both avoids multiplying the force that is applied to the handgrip and avoids the reverse motion-multiplying effect of the collar on the handgrip. Preferably the length of the sleeve substantially exceeds the length of the moment arm to actually reduce the force that is transmitted to the shaft by the sleeve.

The second distinction is the provision of two annular spacers between the crutch shaft and the respective two ends of the sleeve. The two annular spacers are dimensioned radially to take up substantially all of the annular clearance between the shaft and the sleeve. One feature of the preferred practice of the invention is that the two annular spacers are made of yieldable plastic material for a number of purposes: first, to compensate for tolerances in the outside diameter of the shaft and the inside diameter of the sleeve, second, to provide yielding action between the shaft and the sleeve that desirably cushions the loads that are applied to the handgrip, and third, to avoid any snap action between the sleeve and the shaft when the forces that are applied to the handgrip are repeatedly reversed as the handgrip is employed to bear a portion of the users weight and alternately to lift the crutch for a forward stride.

A further feature of the invention in this respect is the concept of employing annular spacers of a plastic material that has a low coefficient of friction with respect to the surface of the crutch shaft. Using annular spacers made of nylon, for example, makes it extremely easy to slide the sleeve along the crutch shaft from one position of adjustment to another.

Further objects of the invention relate to the use of a slidable external sleeve to reinforce a tubular shaft of a crutch. Providing a relatively long external sleeve in the described manner not only reduces the two forces that are transmitted to the shaft from the handgrip and not only increases the spacing longitudinally of the shaft between the two forces, but also reinforces the shaft itself along the substantial length of the sleeve.

Another object of one practice of the invention is to reduce the total mass of metal in the shaft by taking advantage of the reinforcement effect of a relatively long external sleeve. If a shaft were used without the benefit of a relatively long slidable reinforcement sleeve, it would be necessary to make the shaft of a given weight to keep the flexing of the shaft by the users weight within a given degree of deflection. With the sleeve locally reinforcing the shaft, however, the mass of material in the shaft may be substantially reduced to reduce the overall weight and also the overall cost of the crutch without exceeding the given degree of deflection. The weight of the crutch as a whole is reduced by reducing the mass of material of the shaft by a given amount and by employing an effective reinforcement sleeve that weighs less than the given amount. Or the cost of the crutch may be reduced by reducing the cost of the shaft by a given amount and by using a reinforcement sleeve that costs less than the given amount. Or both the cost and the weight may be reduced in this manner.

Viewed from another aspect, a further object of the invention is to improve on a crutch construction wherein the tubular shaft of the crutch has a conventional adjustable handgrip and the tubular shaft is reinforced by a fixed inner steel tube. The improvement consists in transferring the steel reinforcement tube from inside the tubular shaft to the outside of the tubular shaft, placing the handgrip on the external reinforcement tube and providing adjustable latch means to secure the external reinforcement tube at selected positions along the shaft. With this change in the organization of the structure of the crutch, a special advantage is that the reinforcement tube now has the new capability of shifting longitudinally with changes in adjustment in the handgrip so that the spatial relationship between the reinforcement tube and the hand-grip remains constant throughout the range of adjustment of the position of the handgrip.

A still further object of one practice of the invention is to provide an especially strong crutch with a plurality of overlapping reinforcement tubes and with one of the reinforcement tubes at a constant spatial relationship to the adjustable handgrip. In this practice of the invention, the handgrip is mounted on an external slidable reinforcement tube and throughout the range of adjustment of the external reinforcement tube it overlaps two spaced internal reinforcement tubes. The upper of the internal reinforcement tubes may be fixed in the upper end of the crutch shaft to overlap the upper end of the external reinforcement tube throughout the range of longitudinal adjustment of the external reinforcement tube. The lower internal reinforcement tube may be telescoped into the lower end of the crutch shaft in an adjustable manner to serve as means to change the overall length of the crutch and this lower reinforcement tube may extend upward into the range of adjustment of the external reinforcement tube without interferring with the adjustability of the externalreinforcement tube.

In another practice of the invention the slidable sleeve on which the handgrip is mounted extends well below the handgrip to reinforce a substantial portion of the lower half of the shaft in the region where the shaft is stressed to the maximum by the load that is imposed on the handgrip. In such a construction the slidable sleeve may extend a substantial distance above the handgrip and therefore be exceptionally long or, if desired, the handgrip may be on the upper end of a sleeve of lesser length that extends the same distance below the handgrip.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of an axillary crutch embodying the invention;

FIG. 2 is a rear elevational view of the crutch;

FIG. 3 is an enlarged sectional view of the upper end of the crutch as seen along the lines 3-3 of FIG. 2;

FIG. 4 is a section of the handgrip structure taken along the line 44 of FIG. 1;

FIG. 5 is a fragmentary section along the line 5-5 of FIG. 2 showing the means for adjustably anchoring the sleeve on the shaft;

FIG. 6 is a fragmentary longitudinal sectional view taken along the line 66 of FIG. 2 showing the adjustable extension at the lower end of the shaft;

FIG. 7 is a sectional view along the line 77 of FIG. 2 showing the lower end of the shaft;

FIG. 8 is a side elevational view of a forearm crutch embodying a second practice of the invention;

FIG. 9 is a perspective view of the cuff at the upper end of the crutch;

FIG. 10 is a side elevational view of a forearm crutch embodying a third practice of the invention;

FIG. 11 is an enlarged perspective view of the cuff shown in FIG. 10;

FIG. 12 is an enlarged sectional view showing a form of a silencer that may be employed at the two ends of a reinforcement sleeve,

FIG. 13 is an enlarged sectional view of another form of silencer that may be employed;

FIG. 14 is a view similar to FIG. 1 indicating the construction of an exceptionally strong crutch for use by an exceptionally heavy person;

FIG. 15 is a fragmentary sectional view of the handgrip in FIG. 1;

FIG. 16 is a diagrammatic view showing the forces involved in the application of a load to a handgrip that is mounted on an exceptionally short slidable external sleeve;

FIG. 17 is a similar view showing the forces involved when the length of the sleeve is equal to the moment arm of the force that is applied to the handgrip;

FIG. 18 is a similar view showing the forces involved when the length of the sleeve is 25 percent greater than the moment arm; and

FIG. 19 is a similar view showing the forces that are involved when the length of the sleeve is increased to 2.25 times the length of the moment arm.

PREFERRED EMBODIMENTS OF THE INVENTION FIGS. 1 to 7 show the construction of a single shaft axillary crutch having an armrest 20 at the upper end of the crutch and a handgrip 22 at an intermediate level. The single shaft 24 of the crutch is tubular and for adjustment in length is provided with a tubular extension 25 at the lower end which telescopes into the shaft and which is provided in the usual manner with a rubber tip or cushion 26 of well known construction.

As shown in section in FIG. 6, the tubular extension 25 may be provided in its interior with a U-shaped leaf spring 28, one arm 30 of the leaf spring being permanently bonded to the inner wall of the extension with the free arm of the leaf spring carrying a round-nosed locking element 32. The locking element 32 extends through a corresponding radial aperture in the wall of the tubular extension 25 and extends through any one of a row of similar apertures 34 in the shaft 24. Thus to change the effective length of the shaft 24 it is merely necessary to depress the locking element 32 manually to permit the tubular extension 25 to be shifted as desired for engagement of the locking element with a different aperture 34.

As taught by the disclosure of the Wood patent, awkwardness and discomfort on the part of the user is avoided by forming the upper end of the shaft with a curve 35 such that a straight line from the middle of the armrest 20 to the bottom end of the'crutch intersects the handgrip 22. Such a line indicated at 36 in FIG. 1 maybe termed the support axis of the crutch. The inclination of the shaft 24 from the line 36 may be approximately 5 and the line 36 is assumed to be a vertical line when the users weight is balanced on the crutch. The handgrip 22 is perpendicular to line 36 and therefore is at an angle of approximately 95 relative to the shaft 24. It is apparent that the crutch is reversible about the axis 36 and therefore the handgrip 22 may project either forwardly or rearwardly, the handgrip being perpendicular to the axis in each instance.

In accord with the teaching of the invention, the handgrip 22 is rigidly mounted on a relatively long sleeve 40 that slidably embraces the shaft 24 and is adjustable along the length of the shaft. In the construction shown,.the handgrip 22 is rigidly mounted on a collar 42 and the collar, in turn is rigidly mounted on the sleeve 40. As shown in FIG. 4, the collar 42 is formed with an integral radially extending shank 44 which forms the core of the handgrip 22, the core being surrounded by an elastomer casing 45 having an end wall 46. The casing is secured on the core 44 by means of a screw 48 and a cooperating washerSO.

A feature of the invention is that the annular space between the sleeve 40 and the surrounding collar 42 is filled with a suitable adhesive cement that is bonded both to the outer surface of the shaft and to the inner surface of the collar. For this purpose the collar may have one or more radial bores 52 into which a suitable material such as epoxy may be introduced in liquid form. When the epoxy cures it serves in effect to make the core 44 of the handgrip 22 rigidly integral with the sleeve 40.

The sleeve 40 may be adjustable along the length of the shaft 24 in the same manner as the lower extension 25 of the shaft. Thus FIG. 5 shows a U-shaped leaf spring 54 inside the shaft 24 with one arm 55 of the leaf spring permanently bonded to the interior of the shaft and with the free arm of the leaf spring carrying a round-nosed locking element 56. The locking element 56 may selectively engage a series of longitudinally spaced apertures 58 in the sleeve 40.

To make the crutch structurally tight and to prevent any rattling of the sleeve 40 on the shaft 24, suitable annular spacers may be employed to provide snug fit at the opposite ends of the sleeve. For this purpose, FIG. 5 shows how a bushing 60 of suitable resiliently deformable plastic or elastomer may fixedly telescope over each of the two ends of the sleeve with the bushing snuggly but slidingly embracing the shaft 24.

Other types of annular spacers that may be employed at the opposite ends of the sleeve 40 are shown in FIGS. 12 and 13. In FIG. 12 a resiliently deformable plastic or elastomer bushing 62 is similar to the bushing 60 except for the fact that the bushing has an inner circumferential skirt 64 that is tapered in longitudinal cross section to wedge into the annular space between the shaft 24 and the sleeve 40.

In the construction shown in FIG. 13, each end of a sleeve 40a screw-threadedly carries a collar 65 that confines an annular spacer 66 which is made of a suitable resiliently deformable plastic or elastomer. The collar 65 may be of split construction and may be made in two separate halves. One of the circumferential edges of the annular spacer 66 is formed with a bevel 68 and the corresponding end of the sleeve 40a is formed with a chamfer 70 to mate with the bevel 68. In like manner the other circumferential edge of the annular spacer 66 is formed with a bevel 72 and the inner circumference of the collar 65 is formed with an inner circumferential conical shoulder 74 that mates with the bevel 72. It is apparent that tightening the collar 65 on the end of the sleeve 40a not only causes the annular spacer 66 to wedge into the end of the sleeve but also causes the annular spacer to make wedging engagement with the outer end of the collar 65.

The sleeve 40 is at least as long as the'distance from the longitudinal midpoint of the handgrip 22 to the axis of the shaft 24 and the handgrip is spaced a substantial distance from the upper end of the sleeve. In this first embodiment of the invention, the length of the sleeve 40 is approximately five times the length of the moment arm measured from the midpoint of the handgrip.

It is apparent that if the handgrip 22 were adjustably mounted on the shaft 24 by means of a short slidable sleeve in the form of the collar 42, the sleeve 40 being omitted, the moment arm along the handgrip would greatly exceed the length of the collar instead of the length of the collar greatly exceeding the length of the moment arm. Thus, with the handgrip rigidly united with the relatively long sleeve 40 the force-multiplying effect is reversed with consequent drastic reduction of the magnitude of the two opposite forces that are transmitted by the sleeve to the shaft 24 laterally thereof at the opposite ends respectively of the sleeve and, in addition, the space between the two opposite forces measured longitudinally of the shaft is greatly increased. At the same time the slidable sleeve serves as a reinforcement for the shaft and this reinforcement advantageously shifts with adjustment in the level of the handgrip.

It is apparent from the foregoing that if a given shaft is flexed a given amount by a given load applied to a handgrip that is attached to the shaft solely by a relatively short collar, introducing the relatively long sleeve 40 between the collar and the shaft reinforces the shaft so effectively as to greatly reduce the degree to which the shaft is flexed by the given load. Therefore, the invention makes it possible to use a relatively light shaft without the shaft being flexed to an unacceptable degree by the weight imposed on the handgrip.

The second embodiment of the invention shown in FIGS. 8 and 9 is a forearm crutch having a tubular shaft 78 with the usual upper U-shaped cuff 80 and the usual handgrip 82. The U-shaped cuff 80 straddles the upper end of the shaft 78 and is anchored by a bolt 86 that extends through apertures 88 in the cuff and through a diametrical bore (not shown) of the shaft 78, the bolt being provided with a washer 90 and a thumb nut 92.

In the previously described manner, the lower end of the shaft 78 is provided with an adjustable extension 94 that is provided with the usual rubber tip or cushion 95 and a locking element 56 inside the extension 94 is adapted to selectively engage a series of longitudinally spaced apertures 96 in the shaft 78.

The shaft 78 is formed with two opposite bends 96 and 98 which divide the shaft into an upper end portion and a lower end portion and these two opposite end portions of the shaft are at a slight angle relative to each other. The angular relationship of the two opposite end portions of the shaft 78 is such that the support axis that is indicated by the broken line 100 from the middle of the cuff 80 to the lower end of the shaft passes through the handgrip 82. In this instance, however, the handgrip 82 is perpendicular to the upper portion of the shaft instead of being perpendicular to the support axis and the crutch is not reversible.

In the previously described manner, the handgrip 82 is rigidly mounted on a sleeve 102 by means of a collar 104 and the sleeve embraces the upper end portion of the shaft in a slidable manner for adjustment of the position of the handgrip 82. The sleeve 102 is provided with silencers or annular spacers 105 which may be similar to the annular spacer 60 shown in FIG. 5, or may be similar to the annular spacer 62 shown in FIG. 12, or may be of the construction shown in FIG. 13. The sleeve 102 is adjustable longitudinally of the shaft in the previously described manner, a manually retractable locking element 56 releasably interconnecting the sleeve and the shaft.

The sleeve 102 is somewhat shorter than the sleeve 40 in the first embodiment but the length of the sleeve is more than three times the distance from the midpoint of the handgrip 82 to the axis of the shaft 78.

The third embodiment of the invention shown in FIGS. and 11 is a forearm crutch that has a straight shaft 110 to make the construction relatively simple and to reduce the cost of the crutch. The bottom end of the shaft 110 is provided with the usual adjustable extension 112 and rubber tip 114 and the length of the crutch may be changed in the previously described manner by depressing a previously described locking element 32.

The handgrip 115 of the crutch is perpendicular to the shaft 110 and in the previously described manner is mounted on a slidable sleeve 1 16 by means ofa collar 118. The shaft 110 has the usual locking element 56 that may be manipulated for changing the position of the sleeve longitudinally of the shaft.

To make it possible for the support axis represented by the line to intersect the handgrip 115 at a desired distance from the shaft 110, the cuff 122 at the upper end of the shaft is spaced from the shaft by a greater distance than the spacing between the cuff 80 and the shaft 84 in FIG. 8. For this purpose the cuff may be mounted on the upper end of the shaft 110 by means of a casting 123 as shown in FIG. 11. In FIG. 11 the cuff 122 is mounted by rivets 124 to the back of a U-shaped bracket 125 and the bracket in turn is mounted on a wing 126 of the casting 123 by means of a bolt 127.

FIG. 14 indicates the construction of an exceptionally strong crutch to be used by an exceptionally heavy person. The crutch is similar to the first embodiment of the invention shown in FIG. 1, as indicated by the use of corresponding numerals to indicate corresponding parts. The external slidable steel sleeve 40a is exceptionally long and throughout its range of adjustment is in constant overlapping relationship with an internal steel reinforcement tube 130 inside the upper half of the shaft 24a and is in constant overlapping relationship with a lower reinforcement tube which is the extension 25a that is adjustably telescoped into the interior of the shaft 24a. It is to be noted that the lower end 132 of the upper internal reinforcement tube 130 extends well into the upper half of the sleeve 40a and the upper end 134 of the lower extension tube 25a extends well into the interior of the lower end of the sleeve 40a. Since the slidable external tube 40a overlaps both of the internal tubes 130 and 25a throughout its range of adjustment, the two internal reinforcement tubes and the external tube overlap at all times for continuous reinforcement of the shaft 24a from the lower end of the shaft to a point well above the slidable sleeve 40a.

In this last embodiment of the invention the handgrip 22a is mounted on the shaft 24a in the manner shown in FIG. 15. In FIG. 15 a steel shank 135 is rigidly fixed to the sleeve 40a by welding 136 instead of being welded to a short collar that embraces the sleeve. A casing 138 telescopes over the shank 135 and overhangs the outer end of the shank in the same manner as heretofore described with reference to FIG. 4. The casing 138 is secured to the shank in the usual manner by a screw 140.

FIGS. 16 19 are diagrams that make clear the significance of mounting a handgrip 142 on a slidable sleeve that is at least as long as the moment arm that is applied to the handgrip by a load imposed on the handgrip. In FIG. 16 the handgrip 142 is mounted on a relatively short slidable sleeve that is equipped with the usual annular spacers at its opposite ends. The weight of the user of the crutch applies a downward force F at the midpoint of the handgrip 142 and the length of the resultant moment arm measured to the axis of the shaft 145 is a. The downward force F creates a couple comprising a lateral force F at the upper end of the sleeve 144 and an opposite force F at the lower end of the sleeve. With the length of the sleeve 144 equal to only half of the moment arm a the force received by the handgrip is multiplied when it is transmitted to the shaft 145. Thus if the force F is pounds, each of the forces F and F is twice as much or pounds.

In FIG. 17 the handgrip 142 is mounted on a slidable sleeve 146 the length of which is equal to the length of the moment arm a. If the force F is 10 pounds the two transmitted forces F and F are each 10 pounds.

In FIG. 18 the handgrip 142 is mounted on a sleeve 148 that is percent longer than the moment arm a. The applied force of 10 pounds is transmitted to the shaft 145 as two opposite forces of only 8 pounds each.

In FIG. 19 the handgrip 142 is mounted on a slidable sleeve 150 the length of which is 2.25a. Here the applied force of 10 pounds is reduced to two transmitted forces of only 4.45 pounds each.

It is apparent that in progressively increasing the length of the slidable sleeve from the short length in FIG. 16 to the relatively long length in FIG. 19, what may be termed a reversal point is reached, the length of the sleeve at the reversal point being the length of the moment arm a as shown in-FIG. 17. When the length of the slidable sleeve is less than a the force that is applied to the handgrip is multiplied by the slidable sleeve but when the length of the slidable sleeve is greater than a the applied force is reduced by the slidable collar. Thus FIG. 17 illustrates the reversal point where the length of the sleeve is equal to the length of the moment arm. FIGS. 18 and 19 show that increasing the length of the slidable sleeve greatly decreases the two forces that are transmitted by the slidable collar to the shaft and in addition increases the spacing along the shaft between the two applied forces.

My description in specific detail of the selected embodiments of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.

I claim:

1. A crutch including a tubular shaft comprising a first end,

a second end,

a substantially straight portion extending along a first axis 'from said first end to said second end, and

a bent portion, integral with and extending from said second end and angularly related to said first axis, having a distal end,

tubular extension means telescopically mounted on said shaft at said first end and having means for contacting and supporting the crutch relative to a surface being traversed by a user of the crutch,

means for releasably fixing the telescopic relationship between said shaft and said extension means,

first support means mounted on said distal end of said bent portion and defining a second axis passing through said first support means and said contacting and supporting means,

second support means mounted on said tubular shaft and so oriented relative thereto as to intersect both said first and second axes, and

means for adjustably mounting said second support means on said shaft comprising tubular means telescopically mounted on said shaft and having an upper end, a lower end, and a substantially straight portion extending between said upper and lower ends, said tubular means being substantially longer than the moment arm about said first axis of a force applied to said second support means, means for fixing said second support means to said mounting means, and means for releasably fastening said mounting means to said shaft for adjustment of the position of the former along the latter. 2. The crutch of claim 1 including means fixed at said upper and lower ends of said tubular means for reducing play between said tubular means and said shaft.

3. The crutch of claim 1 wherein said first support means comprises armrest means which fits into an armpit of the user of the crutch.

4. The crutch of claim 1 wherein said first support means comprises cuff means which at least partially encircle a portion of the arm of a user of the crutch.

5. The crutch of claim 1 wherein said second axis is closer to the body of a user of the crutch, at the intersection thereof with said second support means, than is said first axis.

6. The crutch of claim 1 wherein the moment arm about said first axis of a force exerted upon said second support means, by a user of the crutch is substantially smaller than the moment arm along said first axis of the resultant force couple exerted by said tubular means on said shaft.

7. A crutch comprising a tubular shaft having a predetermined wall thickness,

a handgrip for attachment to said shaft to support a user of the crutch, and

means for attaching said handgrip to said shaft comprising sleeve means, concentrically mounted on said shaft, to which said handgrip is fixedly attached, said sleeve means having a length, relative to the moment arm of said handgrip about the axis of said shaft, sufficiently greater than said moment arm that damage to said shaft wall, by the force couple exerted on said shaft wall at the opposite ends of said sleeve as a result of a force imposed upon said handgrip, is prevented by a reduction of the size of the forces of the force couple relative to the size of the force exerted on said handgrip. 8. The crutch of claim 7 including means for adjusting the position of said sleeve along the axis of said shaft. 

1. A crutch including a tubular shaft comprising a first end, a second end, a substantially straight portion extending along a first axis from said first end to said second end, and a bent portion, integral with and extending from said second end and angularly related to said first axis, having a distal end, tubular extension means telescopically mounted on said shaft at said first end and having means for contacting and supporting the crutch relative to a surface being traversed by a user of the crutch, means for releasably fixing the telescopic relationship between said shaft And said extension means, first support means mounted on said distal end of said bent portion and defining a second axis passing through said first support means and said contacting and supporting means, second support means mounted on said tubular shaft and so oriented relative thereto as to intersect both said first and second axes, and means for adjustably mounting said second support means on said shaft comprising tubular means telescopically mounted on said shaft and having an upper end, a lower end, and a substantially straight portion extending between said upper and lower ends, said tubular means being substantially longer than the moment arm about said first axis of a force applied to said second support means, means for fixing said second support means to said mounting means, and means for releasably fastening said mounting means to said shaft for adjustment of the position of the former along the latter.
 2. The crutch of claim 1 including means fixed at said upper and lower ends of said tubular means for reducing play between said tubular means and said shaft.
 3. The crutch of claim 1 wherein said first support means comprises armrest means which fits into an armpit of the user of the crutch.
 4. The crutch of claim 1 wherein said first support means comprises cuff means which at least partially encircle a portion of the arm of a user of the crutch.
 5. The crutch of claim 1 wherein said second axis is closer to the body of a user of the crutch, at the intersection thereof with said second support means, than is said first axis.
 6. The crutch of claim 1 wherein the moment arm about said first axis of a force exerted upon said second support means, by a user of the crutch is substantially smaller than the moment arm along said first axis of the resultant force couple exerted by said tubular means on said shaft.
 7. A crutch comprising a tubular shaft having a predetermined wall thickness, a handgrip for attachment to said shaft to support a user of the crutch, and means for attaching said handgrip to said shaft comprising sleeve means, concentrically mounted on said shaft, to which said handgrip is fixedly attached, said sleeve means having a length, relative to the moment arm of said handgrip about the axis of said shaft, sufficiently greater than said moment arm that damage to said shaft wall, by the force couple exerted on said shaft wall at the opposite ends of said sleeve as a result of a force imposed upon said handgrip, is prevented by a reduction of the size of the forces of the force couple relative to the size of the force exerted on said handgrip.
 8. The crutch of claim 7 including means for adjusting the position of said sleeve along the axis of said shaft. 